let nu = null

let obj = {}
let arr = []
let fn = function(){}
let date = new Date()

console.log(str instanceof String); // false 
console.log(num instanceof Number); // false 
console.log(flag instanceof Boolean); //false
// console.log(un instanceof undefined); // 报错
// console.log(nu instanceof null); // 报错
console.log(obj instanceof Object); // ture 

console.log(arr instanceof Object); // ture 

var array = [] // new Array()

//array.__proto__ = Array.prototype

// Array.prototype.__proto = Object.prototype